OK. I've found a rather hacky way of changing the garish red level 0 line color to a much more soothing Fuchsia. I changed line 179 of SynEditMarkupFoldColoring.pas from Colors[0] := clRed; to Colors[0] := $00FF00FF;. Ideally this line would assign the current Keyword color to Colors[0] to give a more coherent color scheme where the color of the keywords is more uniform. (my Keyword color is Fuchsia, by the way!).